The present invention relates to a device for use to prevent human skin from an excessive sunburn caused by ultraviolet radiation.
In general, sunscreen materials such as sun creams, sun oils, sun shades and the like are used to apply to human skin in order to protect the skin from an excessive sunburn caused by ultraviolet radiation. Meanwhile, devices have been proposed which measure a dose of ultraviolet radiation to give an alarm warning the user of an excessive sunburn to her or his skin. This type of the device, for example as described in the specification of U.S. Pat. No. 3,917,948, is used to measure and accumulate the radiation dose of ultraviolet radiation, and to activate an alarm warning the user that the accumulative total has approached or has reached a predetermined radiation dose which may cause sunburns to her or his skin.
On the other hand, various kinds of sunscreen materials such as sun creams, sun oils, sun shades and the like, have been available on the market, which have different indexes indicating an effect for protecting skin from ultraviolet radiation, or the sun protection factor (SPF) values. The sunscreen materials having different SPF values have different skin protection effects i.e. the difference in the SPF values of the sunscreen materials applied to human skins means that total doses of ultraviolet radiation which may cause sunburns to the skins to the same degree are different. The total doses of ultraviolet radiation which may cause sunburns to skins to the same degree depend upon sensitivities of the skins to ultraviolet radiation. Accordingly, the sensitivity of human skin to ultraviolet radiation will be one of the important factors. Human skin is classified into six groups or types depending on the skin sensitivities to ultraviolet radiation and the human skin classification is set forth in Table 1, e.g. ranging from the type I skin having the poorest resistance to ultraviolet radiation to the type VI skin having the highest resistance to ultraviolet radiation.
TABLE 1 ______________________________________ SKIN TYPE DESCRIPTION ______________________________________ I Fair skin Always burns easily Never tans II Fair skin Always burns easily Tans minimally III Light brown skin Burns moderately Tans gradually IV Moderate brown skin Burns minimally Always tans well V Dark brown skin Rarely burns Tans profusely VI Dark brown skin Never burns Deeply pigmented ______________________________________
In Table 2 is set out ultraviolet radiation doses versus each SPF value. Table 2 shows how many times of ultraviolet radiation dose of SPF value "1" can cause sunburns to human skins of various types from I to VI to which no sunscreen material is applied, provided that the ultraviolet radiation dose in "7J/cm.sup.2 " which causes a sunburn to the human skin of type I with no sunscreen material being applied is expressed by the SPF value "1".
TABLE 2 ______________________________________ SPF 7J/cm.sup.2 = 1 1 Type (no sunscreen) 2 4 8 15 ______________________________________ I 1 2 4 8 15 II 2 3 6 12 23 III 2 4 8 16 30 IV 3 5 10 20 30 or above V 4 8 16 30 30 or above or above VI 8 16 30 30 30 or above or above or above ______________________________________
For example, Table 2 indicates that if a sun cream of SPF value "2" is applied to human skin of type I, the ultraviolet radiation dose which can cause sunburns to the above human skin is given by "2", and even though the same sun cream of SPF value "2" is applied to the human skin of type VI, the ultraviolet radiation dose which can cause sunburns to the human skin will be "16", wherein both the ultraviolet radiation doses differ by 8 times. The human skin of type III, to which the sunscreen material of SPF value "1" or no sunscreen material is applied gets sunburnt with an ultraviolet radiation dose of value "2" and the same skin of type III to which the sunscreen material of SPF value "15" is applied gets sunburnt with ultraviolet radiation dose of value "30", as set forth in Table 2. The later is 15 times the former in ultraviolet radiation dose. As above described, the ultraviolet radiation dose which can cause sunburns to skin differs greatly depending upon the types of human skin and the SPF values of the sunscreen materials. In order to surely alarm the user of the above mentioned device to prevent the skin from an excessive sunburn, the SPF value of the sunscreen material applied to the skin and the type of the skin are needed to input to the device. Therefore, a device has been proposed, in which the SPF value of the sunscreen material to be used and the type of skin can be input thereto and an alarm sound is generated at the time the skin has received the ultraviolet radiation dose defined by the SPF value and the skin type. For example, in the specification of U.S. Pat. No. 4,535,244 is described a warning device in which the SPF values of sun creams and the like and sensitivity of skin to ultraviolet radiation have been input to store therein, and when an accumulative total of measured data of ultraviolet radiation dose has reached a specified value determined based upon the input SPF values and skin sensitivity, an alarm sound is generated warning of an excessive sunburn.
In this kind of device, however, the skin sensitivity to ultraviolet radiation is specified for the person who uses the device, so that once the skin sensitivity is set to the device, resetting of the skin sensitivity is not needed thereafter, but in case that sun creams or sun oils having different SPF values are used, an extremely troublesome resetting of the SPF values is needed at each time of application of other sun creams or sun oils having different SPF values. Meanwhile, once a SPF value is set to the device, the device generates an alarm warning the user of an excessive sunburn in accordance with a radiation dose specified based on the set SPF value. Accordingly, there has been another disadvantage that it is inconvenient to use the same and one device among those who apply sun oils and the like of different SPF values.
Taking the purpose of the usage of the device into consideration, it is supposed that the user will take out the device to use it outside. Accordingly it is preferable that the device be made compact in size and light in weight and therefore most of the devices are driven by a battery. Hence, after measuring of ultraviolet radiation, it is necessary to switch the device to its non-measuring mode so as to prevent battery consumption, and if the device is left switched to the measuring mode, the battery is exhausted in vain, resulting in that the device cannot be used when necessary. This is the other disadvantage.